1. Field of the Invention
The present invention relates to Coriolis gyroscopes. In particular, this invention pertains to a Coriolis gyroscope, a system of Coriolis gyroscopes and a method in which, and whereby, quadrature bias is reduced.
2. Description of the Prior Art
Coriolis gyroscopes (vibration gyroscopes, rotation rate sensor) comprise one or multi-part mass systems that are made to vibrate. A first vibration mode (excitation vibration) of the mass system is excited to operate the Coriolis gyroscope. If the Coriolis gyroscope is subjected to rotary motion about its sensitive axis, the Coriolis forces that occur excite a second vibration mode of the mass system, which is detected directly or indirectly, whereby a read-out signal reflecting the second vibration mode is obtained. The read-out signal is analyzed for changes in amplitude which are a measure of the rotation rate applied to the Coriolis gyroscope. In a closed-loop Coriolis gyroscope, a control circuit continuously restores the amplitude of the read-out vibration to a fixed value (e.g. zero) such that the applied rotation rate is derived from the required restoring forces.
The mass system can be designed as a one-part or multiple-part system. It may comprise, for example, two part-masses (resonators) that are coupled to one another by a spring system and can move relative to each other. In a multiple-part mass system, manufacturing tolerances can lead to misalignment (e.g. of the two resonators of a two-part single resonator). The misalignment produces a signal portion that is superimposed in quadrature (90° phase-shifted) over the actual signal portion from the applied rotation rate in the read-out signal of the Coriolis gyroscope. Usually, quadrature signal portions (quadrature bias, quadrature signal, quadrature error) are much larger than those from the desired rotation rate resolution, making the two signal portions difficult to separate. Due to the large difference between the signal portions, even small phase shifts lead to marked noticeable errors in the rotation rate signal (zero-point error, bias).
Known methods to reduce the quadrature bias in a Coriolis mass rotated and/or deflected by a voltage that is applied to specialized control electrodes are described in DE 103 60 962 B4 and DE 102 37 410 A1.
U.S. Pat. No. 6,067,858 describes a structure for reducing quadrature bias that consists of individual correction electrodes. Symmetrical distances must exist between the individual electrodes. Moreover, such structures can be implemented only with buried oxides in the manufacturing process.